JP3194768B2 - Microcapsule and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microcapsule having excellent properties and a method for producing the microcapsule, more specifically, a dense microcapsule excellent in pressure resistance and solvent resistance by an in situ method. And a microcapsule obtained by the method.

[0002]

2. Description of the Related Art A microcapsule is a microsphere having a structure in which a core material is covered with a wall film and having a diameter of about 1 μm to several hundreds μm. It has features such as being able to take out a function when needed and controlling the release of the function.

[0003] By utilizing such properties, the microcapsules include, for example, coating materials for pressure-sensitive copying paper, pharmaceuticals, agricultural chemicals, fragrances, adhesives, enzymes, pigments, dyes, and the like.
It is widely applied as an encapsulant for solvents and the like.

[0004] As a general method for producing the microcapsules, for example, a coacervation method, an interfacial polymerization method,
In situ polymerization methods and the like are well known.

The coacervation method is a method in which a concentrated phase of a polymer is separated from an aqueous solution of a water-soluble polymer in which a core substance is finely dispersed by any method to form a polymer coating on the surface of the core substance. In addition, it is difficult to obtain a capsule slurry having a high concentration, and the encapsulation step is complicated.

In the interfacial polymerization method, a non-water-miscible solvent containing a hydrophobic monomer is finely dispersed in water containing a hydrophilic monomer, and a polymerization reaction is carried out at the interface between the non-water-miscible solvent and water. This is a method of forming a wall film.
However, this interfacial polymerization method has problems that it is difficult to control the polymerization reaction and it is difficult to use a core material having active hydrogen.

On the other hand, the in-situ polymerization method is a method in which a core substance is introduced in a finely dispersed state into a medium, and a monomer contained in either the core substance or the medium is polymerized to form a wall film. There is no limitation on the core material to be encapsulated, and it has the advantage that it can be manufactured with relatively simple operation and at low cost, and has been attracting attention.

In recent years, there has been an increasing demand for the physical properties of microcapsules, and those having excellent resistance to temperature, humidity, and solvents, and having durability and pressure resistance have come to be required. In order to satisfy this requirement, a wall film made of an amino resin is formed by an in-situ method. However, it is difficult to obtain a highly dense coating by a conventional method.

[0009]

SUMMARY OF THE INVENTION The present invention provides a microcapsule having a wall film which is excellent in pressure resistance and solvent resistance and has high tightness, and a method for easily producing the microcapsule by an in-situ polymerization method. It is done for the purpose of.

[0010]

The present inventors have conducted various studies on conditions for forming microcapsules having a wall film having excellent physical properties by an in-situ polymerization method, and as a result, it has been found that hydrolyzed styrene-maleic anhydride is used. A carboxylic acid having two or more carboxyl groups is added to an alkaline aqueous solution of an acid copolymer to make it acidic, and after a hydrophobic core substance is finely dispersed in the aqueous solution, melamine, urea or a mixture of urea and resorcinol is added. By adding an initial condensate with formalin to form a wall film, and then treating the surface of the wall film with water-soluble polyester, microcapsules having excellent pressure resistance, solvent resistance, and a dense wall film can be obtained. The inventors have found that the present invention can be obtained, and have completed the present invention based on this finding.

That is, the present invention relates to a microcapsule comprising a hydrophobic core substance and a wall film, wherein at least the surface of the wall film is formed from a melamine or a precondensate of urea or a mixture of urea and resorcin and formalin with a water-soluble polyester. A polyvalent carboxylic acid is added to a microcapsule composed of a product obtained by a cross-linking reaction and an aqueous solution of a hydrolyzed styrene-maleic anhydride copolymer, and the pH is adjusted to 6
After preparing and dispersing or emulsifying a hydrophobic core substance into fine particles in this aqueous solution, an initial condensate of melamine or a mixture of urea or urea and resorcinol and formalin is added thereto, and the mixture is subjected to acidic conditions. Heat down,
The present invention provides a method for producing microcapsules, which comprises forming a wall film around the microparticles, and then adding a water-soluble polyester to the reaction to cause a reaction, thereby modifying the surface of the wall film. .

In the method of the present invention, the hydrophobic core substance encapsulated in the microcapsules can be a liquid or solid hydrophobic substance conventionally used as the core substance of the microcapsules, and is not particularly limited. Examples of such things include inks, medicines, pesticides, fragrances, adhesives, dyes, solvents, catalysts, enzymes and the like.

In the method of the present invention, first, an aqueous solution of a hydrolyzed styrene-maleic anhydride copolymer is prepared. Regarding the preparation of this aqueous solution, when a powdered styrene-maleic anhydride copolymer is used, the powdered styrene-maleic anhydride copolymer is dispersed in an aqueous medium, and a required amount of alkali is added thereto. In addition, 20-1
After substantially completely hydrolyzing at a temperature of 00 ° C,
It is adjusted to a concentration of about 0.5 to 20% by weight. When a styrene-maleic anhydride copolymer in a solution state (substantially completely hydrolyzed) is used, 0.5 to 20%
It is adjusted to a concentration of about weight%.

The content ratio of styrene units to maleic anhydride units in the styrene-maleic anhydride copolymer used at this time is not particularly limited, but a molar ratio of substantially 1: 1 is preferred. As such a styrene-maleic anhydride copolymer, for example, powdery script set 520 (manufactured by Monsanto) or SMA1000
(Manufactured by Atochem Co., Ltd.), solution-type polymalon (manufactured by Arakawa Chemical Co., Ltd.) and malon (manufactured by Daido Industry Co., Ltd.) are commercially available.

Next, a polyvalent carboxylic acid is added to the aqueous solution of the styrene-maleic anhydride copolymer hydrolyzed in this way to adjust the pH to 6 or less. At this time, it is preferable that the polycarboxylic acid is made into an aqueous solution having an appropriate concentration, and the aqueous solution of the styrene-maleic anhydride copolymer is added little by little while stirring.

By adding the polyvalent carboxylic acid, the aqueous solution of the styrene-maleic anhydride copolymer gradually thickens, and has the highest viscosity in the pH range of 3.0 to 5.5, and has an emulsifying power. Therefore, it is advantageous to add a polyvalent carboxylic acid so that the pH falls within the above range.

The thus obtained aqueous solution of a substantially completely hydrolyzed styrene-maleic anhydride copolymer having a pH of 6 or less serves as an emulsifier and a catalyst for forming a wall film, and serves as an emulsifier. The polymer contributes as one component for forming the wall film.

Examples of the polycarboxylic acid include oxalic acid, citric acid, tartaric acid, malonic acid, maleic acid, fumaric acid, phthalic acid, naphthalenedicarboxylic acid, trimellitic acid, and benzenetetracarboxylic acid.

Next, a hydrophobic core substance is added to the thus obtained aqueous solution of the styrene-maleic anhydride copolymer hydrolyzed to pH 6 or less, and emulsified or dispersed by high-speed stirring or application of ultrasonic waves. Let it. The amount of the core substance at this time is suitably about 5 to 50 times the weight of the styrene-maleic anhydride copolymer based on the weight.

On the other hand, an initial condensate is prepared by condensing a mixture of urea and its resorcinol in an amount of 30 to 50% by weight with formalin. At this time, an initial condensate consisting of a mixture of methylene urea and methylene resorcin is formed by initial condensation under acidic conditions, and an initial condensate consisting of a mixture of methylolated urea and methylolated resorcinol is formed by initial condensation under alkaline conditions. can get. In the case of an initial condensate of melamine and formalin, melamine and formalin are reacted under alkaline conditions.

The precondensate is adjusted to a pH of 8 to 10 by adding an alkali to formalin, for example, and then urea alone or urea and resorcinol in the above ratio is added thereto.
It can be prepared by heating to a temperature of about 100 ° C. At this time, the ratio of formaldehyde to the total amount of urea or resorcin and urea is usually 1.5 mole ratio.
~ 2. The ratio of melamine to formaldehyde is usually selected in a molar ratio of 2 to 6.

Next, the precondensate thus prepared is mixed with a p-side obtained by emulsifying or dispersing the above-mentioned hydrophobic core substance.
In addition to an aqueous solution of a substantially completely hydrolyzed styrene-maleic anhydride copolymer of H6 or less, under acidic conditions of pH 3 to 7, usually at a temperature in the range of 40 to 90 ° C, 30
By reacting while stirring for about 120 minutes, around the microparticles composed of the hydrophobic core material, substantially completely hydrolyzed styrene-maleic anhydride copolymer and the reaction product of the precondensate are removed. Is formed, and a microcapsule dispersion is obtained.

At this time, the amount of the precondensate to be used is selected in the range of 10 to 100 parts by weight per 100 parts by weight of the styrene-maleic anhydride copolymer in terms of solid content.

The wall material of the microcapsule thus formed includes a carboxyl group derived from a hydrolyzate of a styrene-maleic anhydride copolymer and a carboxyl group of a polycarboxylic acid for adjusting pH, Since a functional group such as an amino group or a hydroxyl group derived from the condensate is present, in the present invention, the microcapsule dispersion is further reacted by adding a water-soluble polyester to modify the surface of the wall film. In addition, the wall film is made more excellent in pressure resistance and solvent resistance and highly dense.

The water-soluble polyester is a dicarboxylic acid.
The acid component, the diol component and the monomer having a hydrophilic group
Condensation , hydroxyl group, carboxyl
Having a hydrophilic functional group such as a sil group or a sulfonic acid group
A is, by reacting with functional groups present in the shell material,
Combined with this, a dense coating layer is formed.

Examples of the dicarboxylic acid component include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid and phthalic acid, and aliphatic dicarboxylic acids such as adipic acid, succinic acid, sebacic acid and dodecane diacid. Examples of the components include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, cyclohexanedimethanol, bisphenol A, and the like.

As the hydrophilic monomer, for example, 5-
Examples include dimethyl sodium sulfoisophthalate and polyethylene glycol.

[0028]

According to the present invention, microcapsules having excellent pressure resistance and solvent resistance and having a highly dense wall film can be easily obtained by the in-situ method.

The microcapsules are suitable for safely and reliably protecting, for example, recording materials, pharmaceuticals, agricultural chemicals, fragrances, chemicals, adhesives, foods, dyes, solvents, catalysts, enzymes, and the like.

[0030]

Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

The solvent resistance and pressure resistance of the microcapsules were determined by the following methods.

(1) Solvent resistance 20 cc of each solvent was added to 0.1 g of dry capsules, treated with an ultrasonic cleaner (40 ° C.) for 60 minutes, treated with a membrane filter, and 1 ml of the filtrate was accurately weighed. This was evaporated to dryness, and 2 ml of water was added to obtain a sample solution. Next, the elution% of the core substance in this sample solution was quantified by liquid chromatography to determine the solvent resistance.

(2) Pressure resistance As a load device, Riken Seiki Co., Ltd. (full scale 10
0kg) 10m diameter ram pump as load container
A stainless steel container having a depth of 7 mm and a depth of 7 mm was used. 0.05 g of a sample (primary particles of microcapsules) is accurately weighed into a stainless steel container, covered with a pressure lid, and loaded with a load device.
6.4kg, 12.7kg, 19.1kg or 2 for 0 minutes
After applying a load of 5.5 kg, the container and the pressure lid are placed in a 20 cc sample bottle. Then, 10 ml of tetrahydrofuran was added, and after applying ultrasonic waves for 5 minutes, the solution was filtered through a membrane filter, and the core substance taken out from the broken capsule into tetrahydrofuran was quantified by liquid chromatography, and the breaking ratio (average of three tests) ) Was obtained, and the pressure resistance was evaluated.

Example 1 A 4% by weight aqueous solution of a 100% hydrolyzate of a styrene-maleic anhydride copolymer was prepared, and 16 g of a 30% by weight aqueous citric acid solution was gently added while stirring the aqueous solution. Thereafter, 250 g of dimethyl phthalate was added to 250 g of this aqueous solution and emulsified to prepare an O / W emulsion.

On the other hand, 27.3 g of urea and 9.2 g of resorcin were added to 57.3 g of a formalin solution adjusted to pH 9.0.
Was added all at once, and dissolved at 60 ° C. to prepare pale orange liquid B. Next, this B solution was mixed with the O /
The mixture was gradually added to the W emulsion while stirring, and reacted at 80 ° C. for 2 hours to obtain a dispersion liquid of encapsulated microcapsules having a wall film made of urea-resorcin-formaldehyde resin.

Next, 12.5 g of an aqueous solution of a water-soluble polyester (25% by weight) was dispersed in the dispersion and dried by a spray dryer to produce microcapsules.

The durability and pressure resistance of this product were determined and are shown in Tables 1 and 2, respectively.

Example 2 In Example 1, except that formalin was not adjusted to be alkaline, an anti-microbial antimicrobial capsule was produced in the same manner as in Example 1, and the solvent resistance and pressure resistance were determined. 1 and Table 2.

Example 3 Partial hydrolyzate of styrene-maleic anhydride copolymer 5
An aqueous solution having a concentration of% by weight was prepared, and 250 g of dimethyl phthalate was emulsified in 250 g of the aqueous solution to prepare an O / W emulsion.

On the other hand, 28.0 g of melamine was added at once to 72.9 g of a formalin solution adjusted to pH 9.0,
Solution B was prepared by dissolving at B ° C. Next, this solution B was gradually added to the O / W emulsion while stirring, and
The reaction was carried out at 0 ° C. for 2 hours to obtain an encapsulated microcapsule dispersion having a wall film composed of a melamine-formaldehyde resin.

Next, 12.5 g of an aqueous solution of a water-soluble polyester (25% by weight) was dispersed in the dispersion and dried by a spray dryer to produce microcapsules.

The solvent resistance and pressure resistance were determined, and the results are shown in Tables 1 and 2, respectively.

Comparative Examples 1 to 3 In Examples 1 to 3, no water-soluble polyester was used,
Microcapsules were produced in the same manner as in Example 1 by using the same inclusions as in Examples 1 to 3, and the solvent resistance and pressure resistance were determined. The results are shown in Tables 1 and 2, respectively.

Comparative Examples 4 to 6 In Examples 1 to 3, no water-soluble polyester was used.
Microcapsules were produced in the same manner as in Examples 1 to 3, except that the amount of the inclusions in Examples 1 to 3 was reduced by 10%, and the solvent resistance and pressure resistance were determined.
Shown in

[0045]

[Table 1]

[0046]

[Table 2]

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B01J 13/02

Claims (2)

(57) [Claims] 1. A microcapsule comprising a hydrophobic core substance and a wall membrane, wherein at least the surface of the wall membrane comprises an initial condensate of melamine or a mixture of urea or urea and resorcin and formalin, a dicarboxylic acid component and a dicarboxylic acid component.
Polymer and a monomer having a hydrophilic group.
Water-soluble polyester having a hydrophilic functional group at the molecular end
Microcapsules are composed of those obtained by crosslinking Le. 2. A polycarboxylic acid is added to an aqueous solution of the hydrolyzed styrene-maleic anhydride copolymer to adjust the pH to 6 or less. Then, a hydrophobic core substance is added to the aqueous solution so as to become fine particles. After the dispersion, an initial condensate of melamine or urea or a mixture of urea and resorcinol and formalin is added, and the mixture is heated under acidic conditions to form a wall film around the microparticles.
An acid component, a diol component and a monomer having a hydrophilic group.
Water that has been polycondensed and has a hydrophilic functional group at the molecular end
A method for producing microcapsules, comprising adding a soluble polyester and causing a crosslinking reaction to modify the surface of the wall film.